The present invention relates in general to handpieces for delivering laser radiation from a solid-state laser to biological tissue for the purpose of making a surgical incision therein. The invention relates in particular to a handpiece which is operable to provide a selectively variable spot size of laser radiation at an incision site at a fixed distance from the handpiece.
Laser radiation is used in surgical procedures to make incisions in soft or hard biological tissue. The radiation is generated by a laser apparatus and transported from the laser apparatus to a surgical site by an optical fiber or an articulated arm. Delivery by articulated arm is a preferred method in particular for efficiently transmitting infrared wavelengths such as the 2.94 micrometer (xcexcm) wavelength of the (solid-state) Er:YAG laser. An optical system is typically incorporated in a handpiece attached to the arm for focussing the beam to a spot of a size required for the incision.
The use of laser radiation to make an incision offers an advantage over a conventional surgical incision instrument such as a scalpel or the like in that it can reduce bleeding as a result of the incision because of an attendant cauterization effect. Laser radiation also offers a high degree of flexibility in the kind of incisions that can be made. By way of example, an elongated incision can be made by operating a handpiece to move a fine focussed spot of radiation over tissue in the direction in which the elongated incision is desired. Alternatively, the handpiece can be held steady and the spot delivered thereby held in one position to xe2x80x9cdrillxe2x80x9d a hole in hard tissue or bone. Ability to vary the spot size could provide for an ability to vary the diameter of holes being drilled.
Flexibility and convenience of laser surgical incision would be improved were a handpiece available which could provide a range of beam spot sizes from a beam delivered by a single laser apparatus. A particular problem in providing such a handpiece, however, is that variation of the spot size can require a corresponding variation in laser output power to maintain a constant fluence at the point of incision. In solid-state lasers, variation of the output power typically results in a variation in output beam diameter and divergence (beam quality). There is a need for a handpiece that will not only provide an incision spot of variable spot size but will maintain a selected spot size for a wide range of beam quality in a laser beam delivered to the handpiece.
The present invention is directed to a handpiece for receiving a beam of laser radiation from an optically-pumped solid-state laser via an articulated arm and projecting the radiation onto biological tissue for making an incision therein. The laser beam has a beam quality defined by a value M2 which varies according to the power of optical pumping.
In one aspect, the inventive handpiece comprises an arrangement at a proximal end thereof for attaching the handpiece to the articulated arm for receiving the laser radiation therefrom. An optical system is provided within the handpiece for projecting the received radiation. A probe is provided at a distal end of the handpiece for contacting the tissue being treated. The probe establishes a fixed working distance between the optical system and tissue being treated. The optical system is adjustable for selectively varying the size of a spot of laser radiation projected thereby on the tissue at the fixed working distance from a minimum value to a maximum value, and is arranged such that the size of any selected spot is about the same at any value of M2 between about 1.0 and 15.0.
In another aspect of the inventive handpiece the laser beam has a location therein at which the beam cross-section is about the same at all values of M2. The optical system is arranged to project an image of the invariant cross-section of the laser beam at a fixed distance from the optical system. The projected spot corresponds to the projected image. The effective focal of the optical system is variable for selectively varying the size of the projected spot.
In one preferred embodiment the optical system comprises three optical elements. The fixed distance is measured from a fixed one of the optical elements to the end of the probe, i.e., to the incision site. The other two optical elements are moveable with respect to the fixed optical element for varying the spot size.
The inventive optical system is particularly useful for delivering laser-radiation from an erbium-doped YAG (Er:YAG) laser. Er:YAG has a particularly high thermal lensing coefficient (about 80 diopters per meter per Kilowatt) compared with other solid-state gain media. Accordingly, variations in pump power made to vary output power can lead to substantial variations in M2. The inventive handpiece is able to accommodate such variations while still maintaining a projected spot size at about its selected width.